This invention relates to direct-voltage power supplies, and more particularly to low-noise or low-ripple power supplies.
Much of the advance in standard of living over the past twenty or so years results from the use of advanced communications, data processing, and environmental sensing techniques. The devices used in such communications, processing, and sensing generally become more useful as their sizes are decreased, such that more of them can be used. For example, computers and cellular phones require ever-smaller elements, and become more capable as the number of devices which can be accommodated increases. Similarly, lightweight and reliable sensors can be used in large numbers in vehicles to aid in control and, in the case of spacecraft and military vehicles, to aid in carrying out their missions.
Most modern semiconductor devices, and other devices important for the above purposes, are generally energized or biased by direct voltages. As devices have become smaller, their powering requirements also advantageously decrease. Unfortunately, a concomitant of low power requirements is often sensitivity to unintended noise or fluctuations in the applied power. It is easy to understand that extremely small transistors, which ordinarily operate at two or three volts, could be destroyed by application of tens of volts. It is less apparent but true that small-percentage variations or noise on the applied powering voltage may result in degradation of the operating characteristics of semiconductor and other devices and the circuits in which they operate, which may adversely affect the performance. It is a commonplace that conventional radio and television receivers will respond to noise on or sudden changes in their supply voltages with aural or visual distortions, or both.
In general, electronic equipments require direct voltages for their power sources. There are two general sources of electrical energy which can be used to provide the power, and these two sources are batteries, which provide direct voltage, and power mains of an alternating voltage. When power mains are the source of electrical energy, it is common to rectify the alternating voltage to achieve a direct voltage. The power mains are used to drive machine motors in addition to electronic equipment, so the mains voltages tend to be higher than the voltages required for electronic equipment, and rectified voltages also tend to be higher than desired or usable. In the past, transformers have been used to convert the mains power to voltages more compatible with electronic equipment. However, transformers operating at 60 Hz tend to be much larger than is desirable in modern miniaturized equipment. It might be thought that there are no problems with the powering of electronic equipment from batteries, which directly provide direct voltage. However, batteries have the same general problem as that of mains powering, namely that available direct voltage does not necessarily correspond with the desired operating voltage. One modern technique for producing voltages for powering electronic equipment is that of use of a switching power supply or switching converter, which changes a direct source voltage to a different direct voltage.
A switching power converter can operate from a direct voltage derived from the power mains or from a battery, and can either increase or decrease the output voltage relative to the input voltage. These switching power converters take many different forms, some examples of which include those described in U.S. Pat. Nos. 4,163,926 issued Aug. 7, 1979 in the name of Willis; U.S. Pat. No. 4,190,791, issued Feb. 26, 1980 in the name of Hicks; U.S. Pat. No. 4,298,892 issued Nov. 3, 1981 in the name of Scott; U.S. Pat. No. 4,761,722 issued Aug. 2, 1988 in the name of Pruitt; and U.S. Pat. No. 5,602,464 issued Feb. 11, 1997 in the name of Linkowski et al.
A power supply according to an aspect of the invention powers a load. A storage capacitor is coupled across the load. A first inductance arrangement is coupled to the storage capacitor, which is coupled across the load, to thereby form a combined circuit. A source of voltage produces a direct voltage component and a time-varying voltage component. The source of voltage is coupled to the combined circuit for producing a flow of current therethrough, which flow of current results in division of the direct voltage component and the time-varying voltage component between at least the first inductance arrangement and the storage capacitor coupled across the load, whereby that portion of the time-varying voltage component appearing across the first inductance arrangement tends to cause a time-varying current flow through the first inductance arrangement. A magnetically coupled inductive arrangement is responsive to the time-varying voltage component appearing across the inductance arrangement, for generating a second time-varying current component in response to the time-varying voltage. The second time-varying current component is similar to the time-varying current flow through the first inductance arrangement. A combining arrangement is coupled to the combined circuit and to the magnetically coupled inductive arrangement, for combining the second time-varying current component with at least the time-varying current flow in such a manner as to tend to oppose the time-varying current flow.
In one embodiment, the source of voltage includes a switch which recurrently applies a raw direct voltage to the combined circuit, and applies a reference potential across the combined circuit during those intervals in which the raw direct voltage is not applied, whereby the time-varying component is a rectangular wave.
In another embodiment, of the power supply, the source of voltage comprises a phase-shifted full-wave switched bridge circuit including first and second tap points across which an alternating voltage is generated, and a transformer including a primary winding connected to the first and second tap points. The transformer also includes a secondary winding across which a varying voltage is generated in response to the alternating voltage. The source of voltage also includes a rectifying arrangement coupled to the secondary winding for converting the varying voltage into a varying or pulsating direct voltage.
In one version of a power supply according to an aspect of the invention, the magnetically coupled inductive arrangement comprises an inductive winding magnetically coupled to the first inductive arrangement, whereby the second time-varying current component is directly generated. In another version of a power supply according to this aspect of the invention, the magnetically coupled inductive arrangement comprises a transformer including a primary winding coupled across the first inductance arrangement, and also including a secondary winding across which a secondary voltage is generated in response to the time-varying voltage component appearing across the first inductance arrangement. An inductor or other inductance means is coupled in series with the secondary winding of the transformer, for producing the second time-varying current component in response to the secondary voltage.
A power supply according to an aspect of the invention, in which the first inductance means and the magnetically coupled inductive means responsive to the time-varying voltage component appearing across the inductance means, for generating a second time-varying current component in response thereto, comprises a unitary arrangement, and the unitary arrangement comprises a magnetic core with first and second spaced-apart magnetic paths through which magnetic flux flows. The first inductance means includes a conductor winding about the first magnetic path, and the magnetically coupled inductive means comprising a conductor winding about the second magnetic path. In a first variant of this arrangement, the magnetic core is in the form of two half-cores, each having a cross-sectional shape in the general form of the letter xe2x80x9cU,xe2x80x9d spaced apart by a pair of gaps located at the distal ends of the legs, and the first magnetic path comprises one leg of each of the halves together with one of the gaps, and the second magnetic path comprises another leg of each of the halves together with another of the gaps. In a second variant of this arrangement, the magnetic core is in the form of one of an E or pot core in two halves having legs, where each half has a cross-section in the general shape of the letter xe2x80x9cE,xe2x80x9d which halves fit together with a gap between the center legs of the halves. In this second variant, the first magnetic path includes the center leg of one of the halves of the core, and the second magnetic path includes the center leg of the other one of the halves of the core. In a third variant, the magnetic core is in the form of an E core in two halves, each of which halves has a cross-section defining three legs and a base in the general shape of the letter xe2x80x9cE,xe2x80x9d which halves fit together with a first gap between the center legs of the halves and a second gap between one pair of outer legs. In this third variant, the first magnetic path includes the one pair of outer legs of the halves of the core and the second gap, and the second magnetic path includes the other of the outer legs of the halves of the core and no gap.
In yet another hypostasis of the invention, the combining arrangement comprises a direct-voltage blocking capacitor. This blocking capacitor may be placed in series with the inductive winding of the one embodiment or in series with the secondary winding and inductor of the other embodiment.